Squidlike Creatures Turn Left to Avoid Predators

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Smelling the scents of predators may help the cuttlefish brain
prepare for quick escapes before it even hatches, new research
finds.

The study helps explain why these squidlike cephalopods (and
perhaps other animals) show differences between the two sides of
their brains and bodies — known as lateralization. Lateralization
is the reason most humans favor either their
right or left hands, and many living organisms show some
signs of lateralization.

Clever, color-changing cuttlefish preferentially turn left when
confronted with danger, a side preference that is linked to
differences in visual processing on either side of the cuttlefish
brain. Researchers at the Université de Caen Basse-Normandie in
France wanted to find out how this lateralization develops, and
whether genes or environment play the biggest role.

They first exposed 193 cuttlefish eggs to one of three
conditions: a predator condition, in which the eggs were exposed
to water frequented by dangerous sea bass; a non-predator scent
condition, in which the eggs were exposed to a tank of water
containing harmless sea urchins; and a control condition, in
which the eggs simply sat in plain water. [ Cuttlefish
Cuties: Photos of Color-Changing Cephalopods ]

Three days after the eggs hatched, each
cuttlefish baby was put in a T-shaped tanked filled with
either clean water, sea bass-scented water, or sea-urchin water.
The cuttlefish naturally sought shelter in the arms of the T, and
the researchers recorded in over 10 trials how many times the
cephalopods went left versus right.

The results showed that when the cuttlefish entered water scented
with sea bass, they made for the left more often than for the
right, regardless of where they had incubated when still eggs.
But cuttlefish hatched with the scent of a predator already in
their minds always turned left more often, no matter the scent in
the T-shaped tank. That suggests pre-hatching exposure to
predators makes lateralization stronger.

"This is the first evidence that predation pressure can directly
influence the setting-up of lateralization," study researcher
Christelle Jozet-Alves told LiveScience.

Picking a side and sticking with it may help cuttlefish avoid
indecision in
split-second, life-or-death decisions, Jozet-Alves said.
Lateralization may also help the animals pay attention to things
on both sides of their bodies. For example, Jozet-Alves said, the
left eye may keep an eye out for predator escape routes while the
right eye scans for food.

The findings also show that lateralization is not simply genetic,
but influenced by the pre-hatching environment. If lateralization
were fixed in every cuttlefish at birth, Jozet-Alves said,
predators would likely get savvy to the left-turn defense, so
some flexibility is probably required.

"However, when environmental pressures are high, the advantages
of being lateralized may be far more important than their
disadvantages," she said.

The researchers report their results today (Dec. 11) in the
journal Proceedings of the Royal Society B.